(1) Field of the Invention
The present invention relates to a collective printed circuit board obtained by bonding a plurality of small printed circuit boards each having a mounting unit on which a semiconductor element is mounted to a frame having through holes surrounding the mounting units.
(2) Description of Related Art
Conventionally, in order to simultaneously manufacture a large number of small printed circuit boards to mount semiconductor elements thereon as disclosed in Unexamined Patent Publication No. 1998-189829, Unexamined Patent Publication No. 2001-210954, and Published Japanese Translation No. 2001-511946 of the PCT International Publication (U.S. Pat. No. 6,329,606), a collective printed circuit board is used. In the collective printed circuit board, a plurality of small printed circuit boards are integrally arranged in vertical and horizontal directions such that cutting areas are formed between the small printed circuit boards. On each of the printed circuit boards, after semiconductor elements are mounted through, for example, solder bumps, sealing is performed with a sealing resin. Thereafter, cutting is performed along the cutting areas to simultaneously manufacture electronic devices having semiconductor elements mounted on the printed circuit boards.
In the collective printed circuit board, an electric testing or an appearance check for the printed circuit boards is performed before the semiconductor elements are mounted, and a printed circuit board determined as a defective product is marked, or position information of the defective printed circuit board is recorded. In this manner, a semiconductor element can be avoided from being mounted on the printed circuit board determined as a defective product.
However, in recent years, with advances in miniaturization and multi-layering of circuits of collective printed circuit boards, processes become complicated and difficult, a yield of printed circuit boards in a collective printed circuit board tends to decrease. For this reason, the number of electronic devices that can be simultaneously manufactured from one collective printed circuit board decreases, a problem such as deterioration of operating efficiency and an increase in cost is posed.
In a conventional collective printed circuit board, when sealing is performed with a sealing resin, after the sealing resin is heated to be hardened, the temperature of the sealing resin is returned to a room temperature. At this time, the sealing resin thermally contracts largely more than the printed circuit board. As a result, the printed circuit board is warped such that an upper surface side of the printed circuit board is concaved. This is because a thermal expansion coefficient of the sealing resin is larger than a thermal expansion coefficient of the printed circuit board. When the warpage is large, electronic devices formed by cutting the collective printed circuit board are difficult to be mounted on another circuit board.